Furnaces for burning sewage and like residues

ABSTRACT

The invention provides a furnace for burning sewage comprising a chamber enclosing a pool of the sewage and a burner directed downwardly onto the pool to bathe the whole of the surface of the pool in flame, the pool having a floor which is conical in two stages, so that the area of liquid subject to flame can be controlled by varying the level of the liquid relative to the conical area.

United States Patent 1191 Stribling Mar. 26, 1974 FURNACES FOR BURNING SEWAGE AND 3,482,533 12/1969 Ankersen 110/8 LIKE RESIDUES 3,704,676 12/1972 Davies et al. 110/8 2,592,491 4/1952 Toepel 1. 110/8 [75] In ent r: J hn rian t l g, u n 3,483,832 12/1969 Ball et al 110/7 Coldfield, Warwick, England [73] Assignee: Lucas Furnace Developments Primary ExammerKenneth W. Sprague Lmmed wednesbury England Attorney, Agent, or FirmMarshall & Yeasting [22] Filed: Oct. 26, 1972 Appl. No.1 301,197

Related US. Application Data Continuation-impart of Ser. No. 159,252, 1971, abandoned.

July 2,

U.S..Cl. 110/7 R, 110/8 C Int. Cl. F23g 7/00 Field of Search 110/7 R, 8 R, 8 C, 18 R,

References Cited UNITED STATES- PATENTS Kells et a]. l10/8 [57] ABSTRACT The invention provides a furnace for burning sewage comprising a chamber enclosing a pool of the sewage and a burner directed downwardly onto the pool to bathe the whole of the surface of the pool in flame, the pool having a floor which is conical in two stages, so that the area of liquid subject to flame can be controlled by varying the level of the liquid relative to the conical area.

7 Claims, 4 Drawing Figures 1 FURNACES FOR BURNING SEWAGE AND LIKE RESIDUES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Pat. application Ser. No. 159,252, filed July 2, 1971.

BACKGROUND OF INVENTION This invention relates to furnaces for burning liquid waste such as sewage and like residues.

During the treatment of sewage by certain processes, a liquid is obtained which is a mixture of filtrate and decantrate and has a solids content possibly as high as percent, and the necessity for burning is due to the bacterial and biological characteristics of the liquid. This burning step is difficult both because of the low calorific value of the liquid/solids and also because, in evaporating water from the liquid, an extremely unpleasant smell is generated and there is a danger of contamination from escaping vapours. Similar difficulties arise with other waste liquids containing industrial solvents.

which overcomes these difficulties.

In accordance with the invention, a furnace for burning sewage and the like comprises a chamber and burner means for firing downwardly onto a pool of sewage or the like in the chamber and arranged so that the whole or substantially the whole of the exposed surface of the pool is bathed in flame.

This provides direct heat transfer from flame to liquid at high efficiency due to the turbulence created by the flame avoiding film insulation effects, and ensures that evaporating liquid passes essentially through the flame.

Alternatively the chamber is circular in plan and the burner means fires tangentially and slightly downwardly onto the pool and in a convenient arrangement a plurality of burners is arranged preferably symmetrically, around and slightly above the level of the pool and firing tangentially and downwardly onto the pool.

Preferably the chamber has a valve controlled inlet for the sewage and an exhaust orifice.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation of one embodiment of the invention.

FIG. 2 is a part sectioned elevation of an alternative embodiment;

FIG. 3 is a plan view of the embodiment of FIG. 2; and

FIG. 4 is a further elevation of the embodiment of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawings, the furnace comprises a chamber 1 generally circular in plan, supported by a frame A and having a tank 2 and a detachable frusto-conical roof 3, both made of corrosion resistant metal such as stainless steel for example. The tank is lined with ceramic fibre insulating material 4, and has an inner lining of silicon carbide 5. The roof is also lined with silicon carbide at 6 so that the whole of the chamber interior wall is non-porous and resistant to temperature cycling.

A series of gas or oil burners 7, of heat output in excess of that theoretically required for evaporation and combustion, are disposed with their nozzles arranged at intervals around the chamber and directed generally tangentially and downwardly.

This arrangement bathes the whole surface of the pool of waste, which is located in the chamber, in flame, but produces a pattern of flame and the vapours and combustion products so that the vapours pass upwardly in a central vortex and out through the outlet 10 which is disposed axially above the pool. The remainder of the furnace is the same as that shown in FIG. 1.

The sewage products are led to the chamber 2 by an inlet pipe 14 controlled by a valve 15 which may be operated manually or by automatic means controlled at will or by a thermostat shown at 16, in accordance with furnace temperature, the thermostat being arranged so as to open the valve when a temperature is exceeded and to close the valve when the temperature falls below that temperature. The burners may also be controlled by a thermostat shown at 17 on the outlet pipe.

If desired, the burners may be used to pre-heat the furnace prior to introduction of material to be burnt, and for post-burning sterilisation of the chamber.

In the embodiment of FIGS. 2-4, the hearth or floor of the chamber 2 again has a central rising delivery pipe 20 for liquids to be burnt and this opens into a first frusto-conical space 22 which in turn opens to a second and much shallower frusto-conical space 24 which extends to the chamber side wall 26.

Burners 7 again open tangentially and slightly downwardly and are connected via controls to the fuel supplies and combustion air manifolds 28.

The chamber is generally cylindrical and the height of the cylindrical portion may be slightly more than the diameter: preferably the height/diameter ratio is between 3:4 and 3:2.

Above the cylindrical portion is a frusto-conical cyclone final combustion chamber 30 which opens to offtake duct 32 leading to a scrubber 34 and via a fan 36 to chimney 38.

Waste liquid is fed from tank 40 to a weir tank 42 having a vertically adjustable weir plate 48 so that liquid flows over the plate and is maintained at the same height in the parts 20, 22, 24, as the weir.

In operation, the chamber is pre-heated by burning fuel in the burners and a cyclonic pattern of burning material is induced by the direction of the burners and the combustion air inlets which may be separate from the burners but are similarly directed.

Waste liquid is admitted to a level dependant upon the weir plate (or equivalent means) according to the nature of the waste and the operating conditions in the furnace: thus if the liquid has a high solvent content and the solvent is inflammable and of a high calorific value the level of the surface of the waste will lie within cone 22 and when the burners 7 are shut off will maintain combustion. Cyclonic flow will be maintained by virtue of the combustion air flow, and in the cyclone area 30 this will cause a high efficiency vortex of flame to ensure completion of combustion before the gases leave the furnace.

If however the waste is of low calorific value e.g. if it has a high water content, a larger surface area of burning waste is accommodated by increasing the level height to within cone 24 and at minimum fuel value of the waste, when the burners 7 may require to be run continuously and at high heat input, the pool of waste will occupy the whole area of the cylindrical portion of the furnace.

It is possible to vary the angles of the cones to suit particular needs but it is found experimentally that the use of two cones substantially avoids the need for this, for the narrower angle cone 22 is suitable for high fuel value wastes and the larger angle cone 24 for low ones, and more critical and efficient control is possible by these means than would be the case if for example a single cone were provided.

It is preferred, not only in the case of the embodiment of FIGS. 2-4, but in all cases, to provide sensors in the off take duct for measuring temperature and gas analysis, i.e., determining the CO2 or 02 content.

The temperature sensor is connected primarily to the burners and the waste supply control so that as temperature exceeds a predetermined minimum the burners are shut off and vice versa, and as temperature exceeds a predetermined maximum the weir plate is lowered or the waste delivery pumps are shut off to lower the waste level and hence reduce the combustion rate, and again vice versa, these controls all operating between pre-set limits. Hence the furnace is adapted for automatic variation of combustion rate with a bias towards operating at the maximum rate of waste destruction in most efficient manner, he. at the highest temperature possible having regard to safety and the furnace construction, and with minimum fuel input from the burners.

The CO sensor is particularly useful for controlling the level of the weir plate, or for reducing and increasing, or cutting-off and re-opening the supply of liquid to be burnt in cases where a weir plate is not employed.

' angle: thus when the liquid is one which is difficult to combust the burners may be depressed so that their flame patterns scour the surface of the liquid pool, but when the liquid is easily combustible they may be set more shallowly.

In all embodiments of the invention, any convenient number of burners may be employed, and these may be fired by any suitable means. Multiple inlets and outlets may be provided in place of the single ones shown. The silicon carbide lining referred to may be replaced by other suitable materials.

We claim:

1. A furnace for burning liquid waste, comprising:

a combustion chamber;

a hearth located at the base of said chamber;

a conduit for conducting the liquid waste to be burnt extending beneath the hearth and terminating at an inlet opening provided in the hearth whereby the liquid waste may be introduced into the chamber as a pool covering at least part of the hearth;

a plurality of fuel burners arranged around said chamber above the hearth and all arranged generally tangentially and downwardly to direct flame and combustion products towards the hearth and set up cyclonic action of the combustion products; and an exhaust outlet disposed above the burners so that evaporated liquid waste and products of combustion pass through a hottest zone within the chamber during passage from the hearth surface to the outlet when the burners are operating;

said chamber including a conical cyclone area located between said burners and said outlet for creating a final combustion vortex.

2. A furnace as claimed in claim 1 wherein the hearth surface is frusto-conically-shaped with the smaller diameter end thereof located at a lower level than the larger diameter end thereof and wherein said inlet opening is provided at the smaller diameter end of the hearth.

3. A furnace according to claim 2 including a tank for receiving liquid waste, an overflow weir provided in the tank to maintain the contents of the tank at a predetermined level, said conduit communicating with the contents of the tank, and the upper edge of said weir being located at a level above said inlet opening provided in the hearth whereby the level of waste liquid in the chamber corresponds with said predetermined level.

4. A furnace according to claim 2 wherein the chamber is of cylindrical shape between the hearth and said conical cyclone area and the ratio of height to diameter of the cylindrical portion of the chamber is between 3:4 and 3:2.

5. A furnace according to claim 2 wherein the hearth surface comprises an outer shallow frusto-conical zone and an inner steep frusto-conical zone.

6. A furnace according to claim 5 including a tank for receiving liquid waste, an overflow weir provided in the tank to maintain the contents of the tank at a predetermined level, said conduit communicating with the contents of the tank, and the upper edge of said weir being located at a level above said inlet opening provided in the hearth whereby the level of waste liquid in the chamber corresponds with said predetermined level.

7. A furnace according to claim 5 wherein the chamber is of cylindrical shape between the hearth and said conical cyclone area and the ratio of height to diameter of the cylindrical portion of the chamber is between 3:4 and 3:2. 

1. A furnace for burning liquid waste, comprising: a combustion chamber; a hearth located at the base of said chamber; a conduit for conducting the liquid waste to be burnt extending beneath the hearth and terminating at an inlet opening provided in the hearth whereby the liquid waste may be introduced into the chamber as a pool covering at least part of the hearth; a plurality of fuel burners arranged around said chamber above the hearth and all arranged generally tangentially and downwardly to direct flame and combustion products towards the hearth and set up cyclonic action of the combustion products; and an exhaust outlet disposed above the burners so that evaporated liquid waste and products of combustion pass through a hottest zone within the chamber during passage from the hearth surface to the outlet when the burners are operating; said chamber including a conical cyclone area located between said burners and said outlet for creating a final combustion vortex.
 2. A furnace as claimed in claim 1 wherein the hearth surface is frusto-conically-shaped with the smaller diameter end thereof located at a lower level than the larger diameter end thereof and wherein said inlet opening is provided at the smaller diameter end of the hearth.
 3. A furnace according to claim 2 including a tank for receiving liquid waste, an overflow weir provided in the tank to maintain the contents of the tank at a predetermined level, said conduit communicating with the contents of the tank, and the upper edge of said weir being located at a level above said inlet opening provided in the hearth whereby the level of waste liquid in the chamber corresponds with said predetermined level.
 4. A furnace according to claim 2 wherein the chamber is of cylindrical shape betWeen the hearth and said conical cyclone area and the ratio of height to diameter of the cylindrical portion of the chamber is between 3:4 and 3:2.
 5. A furnace according to claim 2 wherein the hearth surface comprises an outer shallow frusto-conical zone and an inner steep frusto-conical zone.
 6. A furnace according to claim 5 including a tank for receiving liquid waste, an overflow weir provided in the tank to maintain the contents of the tank at a predetermined level, said conduit communicating with the contents of the tank, and the upper edge of said weir being located at a level above said inlet opening provided in the hearth whereby the level of waste liquid in the chamber corresponds with said predetermined level.
 7. A furnace according to claim 5 wherein the chamber is of cylindrical shape between the hearth and said conical cyclone area and the ratio of height to diameter of the cylindrical portion of the chamber is between 3:4 and 3:2. 